The present invention relates to a hybrid drive system.
In recent years, hybrid vehicles having an engine and a rotating electric machine (a motor or a generator) as drive power sources are gaining attention from the viewpoints of energy savings and environmental issues. Various arrangements have been proposed for hybrid drive systems used in the hybrid vehicles. Many of these hybrid vehicles, even without having a rotating electric machine dedicated to starting the engine, permit the engine to be started using a rotating electric machine for driving the vehicle. Japanese Patent Application Publication No. JP-A-09-170533, for example, discloses a hybrid drive system that allows an engine to be started using a rotating electric machine for driving a vehicle.
In other words, the system disclosed in Japanese Patent Application Publication No. JP-A-09-170533 is a so-called split-type hybrid drive system including an engine operated by the combustion of a fuel, a distribution mechanism mechanically distributing an output of the engine to a first rotating electric machine and an output member, and a second rotating electric machine applying a rotating force between the output member and a drive wheel. The hybrid drive system is arranged to start the engine by using the first rotating electric machine that rotatably drives the engine through the distribution mechanism. The hybrid drive system further includes a driving force fluctuation inhibition unit that inhibits a vehicle driving force from fluctuating, which would otherwise be caused by a reaction force acting on the output member when the engine is started or the like. The driving force fluctuation inhibition unit is a parking lock unit that mechanically prevents the wheel from rotating through a parking operation performed by a driver or a startup timing motor controller that controls the second rotating electric machine so as to offset fluctuations in the driving force caused by engine starting.